(i) Field of the Invention
The present invention relates to a receiver which is applicable to a plurality of mobile radio communication systems by one unit and which receives a signal while switching the communication system and, more particularly, to a receiver in which a circuit scale is reduced to intend the miniaturization of a device.
(ii) Description of the Related Art
As communication systems used for a mobile radio cellular system, for example, there are a time division multiple access (TDMA) system, a frequency division multiple access (FDMA) system, and code division multiple access (CDMA) system.
A receiver for such a plurality of communication systems (hereinbelow, simply referred to as a receiver) which has a function for receiving signals of the plurality of communication systems and can receive a signal by switching to one communication system arbitrarily selected will now be described.
A conventional receiver will now be explained with reference to FIG. 13. FIG. 13 shows a constructional block diagram of the conventional receiver.
As shown in FIG. 13, the conventional receiver comprises an antenna 1, a gain variable LNA (low noise amplifier) 2, an AGC (automatic gain control) control unit 6, a mixer 8, an LPF (low pass filter) bank 9xe2x80x2, a switching circuit 10, an A/D converter 11, a demodulating unit 12xe2x80x2, a control unit 13xe2x80x2, and a variable oscillator 21.
The component elements of the conventional receiver will now be explained hereinbelow.
The antenna 1 is a receiving antenna.
The gain variable LNA 2 is an LNA (Low Noise Amplifier) which can control a gain.
The AGC control unit 6 controls the gain of the gain variable LNA 2 so that a received signal level in an output of the switching circuit 10, which will be described herein later, is set constant.
The variable oscillator 21 is a variable oscillator for outputting a signal having the same local frequency as a carrier frequency used in the communication system in accordance with a frequency control signal from the control unit 13xe2x80x2 which will be described herein later.
The mixer 8 frequency converts an input signal to a base band signal by a local oscillation frequency supplied from the variable oscillator 21.
The low pass filter (LPF) bank 9xe2x80x2 is a bank having LPFs 9-1 to 9-n through which signals of bands used in the communication systems can pass in accordance with the plurality of applicable communication systems.
The switching circuit 10 receives all of outputs from the LPFs 9-1 to 9-n and outputs only the output from the LPF 9 designated in accordance with a switching control signal to designate the LPF 9 to be used on the basis of the communication system selected by the control unit 13xe2x80x2, which will be described herein later, to the post stage.
The A/D converter 11 converts the output from the selected LPF 9 to a digital signal.
The demodulating unit 12xe2x80x2 has demodulating functions in the plurality of applicable communication systems and performs demodulation by selecting the demodulating function of the designated communication system in accordance with a demodulating unit control signal to designate the communication system outputted from the control unit 13xe2x80x2 which will be explained hereinbelow.
The control unit 13xe2x80x2 outputs the frequency control signal to designate the same local frequency as a carrier frequency used in the communication system to the variable oscillator 21 in accordance with the one communication system arbitrarily selected from the outside, outputs a switching control signal to switch the LPF 9 which is applicable to the communication system to the switching circuit 10, and further, generates the demodulating unit control signal to designate the communication system to the demodulating unit 12xe2x80x2.
The operation of the conventional receiver will now be described with reference to FIG. 13.
In the conventional receiver, the frequency control signal to designate the same local frequency as the carrier frequency used in the communication system is outputted to the variable oscillator 21 by the control unit 13xe2x80x2 in accordance with the arbitrary communication system selectively inputted from among a plurality of applicable communication systems from the outside. A signal having the designated frequency is oscillated to the mixer 8 by the variable oscillator 21.
The switching control signal of the LPF 9 suitable to the selected communication system is outputted from the control unit 13xe2x80x2 to the switching circuit 10. Further, the demodulating unit control signal to designate the demodulation system based on the selected communication system is outputted from the control unit 13xe2x80x2 to the demodulating unit 12xe2x80x2.
A received signal received by the antenna 1 is amplified by the gain variable LNA 2 and the resultant signal is frequency converted to a base band signal by the mixer 8 by using a signal which is outputted from the variable oscillator 21 and which has the same local frequency as the carrier frequency used in the designated communication system. The resultant signal is fetched to all of the LPFs 9 in the LPF bank 9xe2x80x2. Only bands used in the communication systems are outputted from the LPFs 9.
In accordance with the communication system selected by the switching circuit 10, only the output from the LPF 9 designated by the control unit 13xe2x80x2 is outputted to the A/D converter 11.
At that time, the signal passed through the switching circuit 10 is fetched to the AGC control unit 6 and the gain of the gain variable LNA 2 is controlled by the AGC control unit 6 so that the level of the signal is held constant.
The signal is converted to a digital signal by the A/D converter 11 and the resultant signal is demodulated by the demodulating unit 12xe2x80x2 by the communication system selected in accordance with the demodulating unit control signal from the control unit 13xe2x80x2.
As a conventional technique in which a plurality of communication systems are properly used by using a plurality of band pass filters having different characteristics, for example, there are a xe2x80x9cFrequency Band Switching Common Devicexe2x80x9d proposed in Japanese Patent Application Laid-Open No. 10-247861(1998) disclosed on Sep. 14, 1998 (Applicant: Kokusai Electric Co., Ltd., Inventor: Katsumi Tanaka et al.) and an xe2x80x9cAntenna Common Devicexe2x80x9d proposed in Japanese Patent Application Laid-Open No. 10-41704(1998) disclosed on Feb. 13, 1998 (Applicant: Goyo Electronics Co., Ltd., Inventor: Masahiro Shindo et al.).
Each of those conventional techniques relates to a cellular phone of such a dual mode that an analog system and a digital system share the same frequency band, in which a plurality of filters are used in a reception side.
In the above conventional receiver, however, it is necessary to individually prepare the LPF 9 every corresponding communication system, so that there is a problem that a circuit scale remarkably increases.
It is an object of the present invention to provide a receiver for switching a plurality of communication systems to receive a signal, in which a circuit scale is reduced to intend the miniaturization of a device.
According to the present invention, there is provided a receiver which can be applicable to a plurality of communication systems and which receives a signal by the communication system arbitrarily selected from among the plurality of communication systems, comprising converting means for converting a received signal to a base band signal by a local oscillation frequency based on the selected communication system, setting means for setting a peculiar tap coefficients based on the selected communication system, and synthesizing means for weighting the base band signal with the set tap coefficients to synthesize them, and demodulating means for the signal synthesized by weighting by a demodulation system based on the selected communication system. Since it can be applicable to the plurality of communication systems without providing a band pass filter every communication system, a circuit scale can be reduced.
According to the present invention, there is provided a receiver which can be applicable to a plurality of communication systems and which receives a signal by the communication system arbitrarily selected from among the plurality of communication systems, comprising a variable oscillator for oscillating a local oscillation frequency based on the selected communication system, a mixer for converting a received signal to a base band signal by the local oscillation frequency, a transversal filter for setting a tap coefficient from information of tap coefficient inputted from the outside based on the selected communication system, and weighting the base band signal with the tap coefficient to synthesize them, thereby performing a band limitation based on the communication system to the resultant signal, and a demodulating unit for demodulating the signal by a demodulation system based on the selected communication system. Since it can be applicable to the plurality of communication systems without providing a band pass filter every communication system, a circuit scale can be reduced.
According to the present invention, there is provided a receiver which can be applicable to a plurality of outside communication systems and which receives a signal by the communication system arbitrarily selected from among the is plurality of communication systems, comprising a receiving antenna, a gain variable LNA for amplifying a signal from the receiving antenna by a gain control signal inputted from the outside, a mixer for converting a frequency of an output of the gain variable LNA to a base band frequency band by using a signal having a local frequency inputted from the outside, a variable oscillator for supplying a signal having the local frequency designated from the outside communication system to the mixer, an LPF, which has a band through which a signal having the widest band among the plurality of communication systems can pass, for limiting a band of the signal that is frequency converted by the mixer, an AGC control unit for deciding a gain of the gain variable LNA from the output of the LPF and generating a gain control signal to the gain variable LNA, a transversal filter for setting a tap coefficient from information of the tap coefficient inputted from the outside on the basis of the selected communication system and performing a band limitation suitable to the demodulation system based on the communication system by weighting the output of the LPF with the tap coefficient for synthesis, a demodulating unit for receiving the band-limited signal outputted from the transversal filter and performing demodulation based on the selected communication system to the signal, and a control unit for designating a local frequency of the variable oscillator on the basis of the selected communication system, outputting information of the tap coefficient having a fixed length that is equal to the maximum number of taps in the plurality of communication systems to the transversal filter so as to enable to be applicable to all of the plurality of communication systems, and designating a demodulation system to the demodulating unit. Since it can be applicable to the plurality of communication systems without providing a band pass filter every communication system, a circuit scale can be reduced.
The transversal filter according to the present invention suitably comprises sample holding means for sampling outputs of the LPF and holding a plurality of sampling values, delay means for subsequently shifting the information of tap coefficients supplied from the outside to hold them and for outputting the held information as a tap coefficient while shifting the information, synthesizing means for obtaining the sum of products obtained by multiplying the tap coefficients outputted from the delay means by sampling values outputted from the sample holding means and then outputting the sum, and timing control means for performing timing control in the sample holding means and the delay means.
The sample holding means of the transversal filter is means having sample holding circuits of the same number as that of predetermined sampling values and a first switch for sequentially sorting the outputs from the LPF to the sample holding circuit. As sample holding circuits, a sample holding circuit comprising a pair of second and third switches which are connected in series and which perform opening and closing operations for a clock signal so as to be contrary to each other, a capacitor for holding output signals of the switches, and a buffer for temporarily holding an input signal and signals held by the capacitor, sampling analog signals sorted and supplied by the first switch by the switching operations of the second and third switches, holding, and then outputting the signals is suitably used. The sample holding circuit can sample and hold input signals by a simple construction using switches, capacitor, and buffer and the switching operations of the switches.
The delay means of the transversal filter has serially connected delay elements of the same number as that of the sampling value. Each delay element holds information of the inputted tap coefficient. The delay means for simultaneously outputting digital values held in the delay elements as tap coefficients synchronously with a clock timing while shifting each value by an amount as much as one delay element is suitably used. The delay means can output the tap coefficients by a simple construction using the delay elements.
The synthesizing means of the transversal filter is synthesizing means having multiplying circuits of the same number as that of sampling values and an adding circuit for adding outputs from the multiplying circuits. As a multiplying circuit, a multiplying circuit having impedances which are connected in parallel and to which the inputted sampling value is dividedly supplied, switches each of which is connected to each impedance in series and which opens or closes by a value of each bit constructing the inputted tap coefficient, an amplifier to which outputs from the switches are supplied, and a feedback impedance for feeding back an output of the amplifier is suitably used. The synthesizing means can weight the sampling value with the tap coefficient to synthesize them by a simple construction using the impedances, switches, and feedback amplifier.
According to the present invention, there is provided a receiver having an A/D converter for converting an output from the transversal filter to a digital signal and a program section for realizing functions of the demodulating unit and control unit by using software in place of the above units. Since it can be applicable to a plurality of communication systems without having a band pass filter every communication system, a circuit scale can be reduced.